1. Field of the Invention
The present invention relates to a liquid-crystal display device comprising a planar microlens array and a liquid-crystal display panel which are combined with each other.
2. Description of the Related Art
FIG. 1 of the accompanying drawings shows a conventional liquid-crystal display device which comprises a planar microlens array 100 and a liquid-crystal display panel 200 which are combined with each other. As shown in FIG. 1, the planar microlens array 100 has a base glass plate 101, an array of convex microlenses 102 disposed on a surface of the base glass plate 101, and a cover glass plate 103 bonded to the array of convex microlenses 102 by an adhesive layer 104. The liquid-crystal display panel 200 has a glass substrate 201 spaced from the cover glass plate 103 by a spacer 201a, with a liquid crystal layer 202 filled between the cover glass plate 103 and the glass substrate 201. The glass substrate 201 supports transparent pixel electrodes 203 on its surface facing the liquid crystal layer 202. The surface of the glass substrate 201 includes portions 204 that are free of the transparent pixel electrodes 203 and carry interconnections and TFTs (Thin Film Transistors) which do not transmit incident light. Electrodes 205 which confront the transparent pixel electrodes 203 are mounted on a surface of the over glass plate 103 that faces the liquid crystal layer 202.
The adhesive layer 104 which is filled between the array of convex microlenses 102 and the cover glass plate 103 needs to be made of a material, i.e., a synthetic resin, having a refractive index that is sufficiently smaller than the refractive index of the material, i.e., a synthetic resin, of which the array of convex microlenses 102 is made.
However, synthetic resins which are presently available in the art for use as the material of the adhesive layer 104 do not have sufficiently low refractive indexes, leaving much to be improved with respect to the numerical aperture of the array of convex microlenses 102.
This problem will be illustrated below in reference to the fabrication of a lens that is required to have a certain numerical aperture. If the difference between the refractive index of the lens and the refractive index of a material held in contact with a curved surface of the lens is too small, then it is necessary to reduce the radius of curvature of the lens surface, making the lens shape closer to a hemispherical shape in order to attain the desired numerical aperture. However, the reduced radius of curvature of the lens surface results in an increased spherical aberration. With the increased spherical aberration, the lens tends to focus applied light into a larger light spot.